Instrumentation and associated methods for joint prosthesis implantation

ABSTRACT

An assembly for preparing a vertebral disc space to receive a prosthesis comprises a support frame having a base and a pair of guide tracks extending from the base. The base is adapted to attach to a plurality of vertebral bodies. The assembly further includes a guide block operatively connected to at least one of the guide tracks and having an opening disposed there through. The assembly further includes a position control mechanism corresponding to the at least one of the guide tracks. The position control mechanism has a plate extending there from for coupling to the guide track and the guide block and an actuating knob for adjusting the position of the plate and therefore the guide block. The assembly further includes a bone-removal device positioned through the opening of the guide block and operatively connected to the guide block.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application No.10/303,569, filed Nov. 25, 2002 and entitled “Implantable JointProsthesis And Associated Instrumentation,” which claims priority to theprovisional application filed on Nov. 26, 2001 (Ser. No. 60/333,627).The above referenced applications are herein incorporated by referencefor all legitimate purposes.

BACKGROUND

According to one embodiment, implantable prostheses are provided thatare suitable for replacement of diarthroidal or arthroidal joints bycreating an artificial diarthroidal-like joint at the site of theimplant.

In a particular embodiment, an implantable prosthesis is describedserving as a replacement for at least a portion of the intervertebraldisc material, i.e., a spinal disc endoprostheses suitable forimplantation in vertebrates, including humans.

In another embodiment, an assembly with associated instrumentation isdescribed for preparing a disc space for the insertion of a prosthesis.

Many joints in the human body, such as hips, knees, shoulders, etc., arediarthroidal, meaning that the joints include ajoint capsule that isfilled with fluid. The capsule fluid lubricates the joint, and allowsthe surfaces of the joint to move with a low coefficient of friction.The spine, by contrast, can be considered to be a series of joints, someof which (the anterior joint or disc) lack a fluid filled capsule andare therefore arthroidal (the spine also contains facet joints that arediarthroidal). The interior portion of intervertebral discs are notprovided by the body with significant blood supply; their homeostasis isenhanced by the diffusion of fluids into the disc tissue, thus supplyingthem with nutrients. This, to some extent, allows the tissue to grow andrepair damage done by stress as the joint moves. Despite this process,in mature adults, spinal disc tissue degrades continuously over time.Sufficiently advanced degeneration can lead to herniation or rupture ofthe spinal disc.

Herniation of a spinal disc can result in a number of debilitatingsymptoms, including intractable pain, weakness, and sensory loss.Treatment of these symptoms frequently requires surgical removal of atleast a portion of the herniated disc, a procedure known as discectomy.Often discectomy alone cannot stop the progressive degeneration at thelevel of disc excision. An additional procedure is often performed inconjunction with the discectomy with the objective of fusing together(arthrodesis) the vertebral bodies surrounding the affected disc space.This is accomplished by removing the cartilaginous endplates by scrapingthe surfaces of the vertebral body and inserting a piece of graft bone,which may be an allograft from a bone bank, or an autograft, typicallytaken from the iliac crest of the patient, or other suitable material.

The discectomy and arthrodesis procedures can be problematic, however.Discectomy problems have been described above. The grafting or fusionprocedure has a variable success rate of about 80%, and even whensuccessful, requires considerable recovery time before fusion iscomplete. Perhaps of even greater concern, successful fusion eliminatesnormal spinal biomechanics. Range of motion at the level of the fusionis ideally eliminated, because the affected vertebrae have beeneffectively joined to form a single bone. Because the patient tries tomaintain the same overall range of motion of the entire spine,additional stress is imposed on the intervertebral discs of the adjacentvertebrae. This, in turn, may lead to accelerated degeneration at levelsabove and below the fusion site, which may require additional treatment,including discectomy and fusion. Grafting procedures carry some risk oftissue rejection and disease transmission if an allograft is used, andrisk of harvest site morbidity when the patient's own tissue isharvested.

As a result of these difficulties with intervertebral fusion, attemptshave been made to provide a prosthetic solution to degenerative discdisease that maintains the patient's normal spinal biomechanics, allowsfor shorter recovery times, and avoids the complications inherent inharvesting and/or grafting bone tissue. Some of these efforts havecentered around providing an endoprosthetic intervertebral implant, asdescribed in U.S. Pat. Nos. 5,865,846, 5,674,296, 5,989,291, 6,001,130,6,022,376, and pending U.S. patent application Ser. No. 09/924,298,filed on Aug. 8, 2001, the entire contents of which are herebyincorporated by reference.

Design and construction of such an implant, however, is not simple.Desirably, the implant should be precisely placed in a preparedintervertebral space, and should contain elements that are immobilizedwith respect to each of the vertebral bodies, so that the implant doesnot migrate or shift, potentially contacting, abrading, or otherwisedamaging the spinal cord, ligaments, blood vessels, and other softtissue. At the same time, the implant should allow the vertebral bodiesto move relative to each other in a way that provides the equivalentmotion afforded by a healthy intervertebral disc, and that allows theaffected vertebral joint to participate in the coordinated overallmovement of the spine in a way that closely approximates the naturalmovement of a healthy spinal column. The implant should bebiocompatible, and avoid the introduction of toxic or harmful componentsinto the patient, such as release of wear debris. The implant shouldalso restore normal disc height and maintain the patient's vertebrallordosis, and should not allow any significant post-operativesubsidence. The implant should be at least partially constrained by softtissue in and around the intervertebral space, in order to allow asimpler, more efficient design. There remains a need for a device whichwould decrease patient recovery time, and reduce the occurrence ofpostoperative degeneration at levels above and below the implant, ascompared with fusion techniques. In addition, such an implant wouldavoid the need for harvesting of autograft bone tissue, therebyeliminating morbidity at the harvesting site. Such an implant shouldalso provide elasticity and damping sufficient to absorb shocks andstresses imposed on it in a manner similar to that of the natural spinaldisc.

Furthermore, specially designed instrumentation should be provided tofacilitate the precise placement of the implant. The instrumentationshould facilitate accurate preparation of the vertebral body endplatesto receive the implant, but should be minimally obtrusive of thesurgeon's view of the operating site. The instrumentation should beadapted for use in an anterior surgical approach to the lumbar spinewhere there are numerous structures that are at risk, and which ifdamaged could cause severe complications.

SUMMARY

This invention satisfies the needs and concerns described above. In oneembodiment, an assembly for preparing a vertebral disc space to receivea prosthesis is provided. The assembly comprises a support frame that isadapted to attach to a plurality of vertebral bodies. A guide blockhaving an opening disposed there through may operatively connect to thesupport frame. A position control mechanism may further be provided forcontrolling the position of the guide block relative to the supportframe. A bone-removal device may be positioned through the opening ofthe guide block and operatively connect to the guide block. Thebone-removal device may comprise a tool having a bone-removal elementextending from the tool.

In another embodiment, an assembly for preparing a disc space forimplantation of a prosthesis may comprise a sagittal wedge adapted to bedisposed between a pair of vertebral bodies. A support frame and a discspacer clip may be positioned over the sagittal wedge. A tilting guidemember may be adapted to be positioned in the disc spacer clip. Atransverse unit for mounting to the tilting guide member may be providedfor accommodating a bone-removal tool.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective drawing of an intervertebral endoprosthesis inaccordance with one embodiment.

FIG. 2 is an elevational view of the intervertebral endoprosthesis shownin FIG. 1.

FIG. 3 is a top plan view of the intervertebral endoprosthesis shown inFIG. 1 and 2.

FIG. 4 is an isometric cross sectional view of the intervertebralendoprosthesis shown in FIG. 1, 2, and 3.

FIG. 5 is a plan view of an implant plug and plug installation tool usedto insert a plug into an intervertebral endoprosthesis.

FIG. 6 is a sectional view of the intervertebral endoprosthesis shown inFIG. 1-4.

FIG. 7 is an exploded perspective view of the intervertebralendoprosthesis shown in FIG. 1-4 and 6.

FIG. 8 is a plan view (A) and sectional view (B) of one embodiment of anintervertebral endoprosthesis undergoing lateral bending.

FIG. 9 is a plan view (A) and sectional view (B) of one embodiment of anintervertebral endoprosthesis undergoing translation.

FIG. 10 is a plan view (A) and sectional view (B) of one embodiment ofan intervertebral endoprosthesis undergoing lateral bending.

FIG. 11 is a plan view (A) and sectional view (B) of one embodiment ofan intervertebral endoprosthesis undergoing translation.

FIG. 12 is a perspective view of one embodiment of an intervertebralendoprosthesis, particularly suitable for lumbar use.

FIG. 13 is an anterior-posterior cross-sectional schematic view of theintervertebral endoprosthesis of FIG. 12.

FIG. 14 is a side perspective view of the implanted endoprosthesiscorresponding to FIG. 13.

FIG. 15 is a front schematic view of the implanted endoprosthesis withone of the vertebral bodies cut away.

FIG. 16 is a top schematic view of one embodiment of an implantedendoprothesis.

FIG. 17 is a top schematic view of one embodiment of an implantedendoprothesis.

FIG. 18 is an anterior-posterior cross-sectional schematic view of animplanted endoprosthesis.

FIG. 19 is a schematic view of surgical instruments suitable forimplanting an intervertebral endoprosthesis, such as that of FIG. 12.FIG. 19A is a schematic view of a bone removal device and associatedsupport frame, and position guide block, and other instruments. FIG. 19Bis a perspective view of a position guide block shown in FIG. 19A.

FIG. 20 is a schematic perspective view of a bone removal devicesuitable for use in implanting the intervertebral endoprosthesis of FIG.12.

FIG. 21 is a schematic cross-sectional view of an embodiment of a boneremoval instrument similar to the instrument shown in FIG. 20.

FIG. 22 is a schematic diagram illustrating the use of a bone removalinstrument to remove bone from a vertebral body.

FIG. 23 is a schematic perspective view of a distal end of a sagittalwedge used in an alternative embodiment.

FIG. 24 is a schematic perspective view illustrating a sagittal wedge asshown in FIG. 23 inserted between two vertebral bodies.

FIG. 25 is a perspective view of the distal end of a support frame usedin the implantation of an intervertebral endoprosthesis in oneembodiment.

FIG. 26 is a perspective schematic view of the support frame of FIG. 25disposed over the sagittal wedge of FIG. 23, which is disposed betweentwo vertebral bodies.

FIG. 27 is a perspective view of a disc spacer clip used in implantingan intervertebral endoprosthesis.

FIG. 28 is a schematic perspective view showing placement of the discspacer clip of FIG. 27 relative to the support frame, sagittal wedge,and vertebral bodies.

FIG. 29 is a schematic perspective view showing the arrangement of thedisc spacer clip, support frame (including brace connector), andvertebral bodies after removal of the sagittal wedge.

FIG. 30 is a perspective view of a tilting guide member used inimplanting an intervertebral endoprosthesis.

FIG. 31 is a schematic perspective view showing the arrangement of thetilting guide member of FIG. 30 with respect to the support frame, discspacer clip, and vertebral bodies.

FIG. 32 is a perspective view of a transverse unit used in implantingthe intervertebral endoprosthesis. FIG. 32A is a perspective view of theentire transverse unit, while FIG. 32B is a close-up perspective view ofan assembly of a central member and inner member of the transverse unit.

FIG. 33 is a schematic perspective view showing the arrangement of thetransverse unit of FIG. 32 with respect to the assembly of FIG. 31.

FIG. 34 is a close-up perspective view of the arrangement of FIG. 33,showing the proximal transverse block of the transverse unit.

FIG. 35 is a close-up perspective view similar to that of FIG. 34,showing the disposition of a bone removal device relative to thetransverse unit.

FIG. 36 is a close-up schematic perspective view showing the dispositionof a bone removal device relative to the transverse unit, support frame,disc spacer clip, tilting guide member, and vertebral bodies.

FIG. 37 is a schematic perspective view showing the arrangment of thebone removal device and transverse unit, as well as pivot tool 396.

FIG. 38 is a schematic perspective view of two embodiments ofintervertebral endoprostheses. FIG. 38A shows an intervertebralendoprosthesis having a more rounded shape, while FIG. 38B shows anintervertebral endoprosthesis having a more rectilinear shape.

The invention can be more clearly understood by reference to some of itsspecific embodiments, described in detail below, which description isnot intended to limit the scope of the claims in any way.

DETAILED DESCRIPTION

In general, a prosthetic device is provided for replacing a human bonejoint and instrumentation designed to facilitate the precise positioningof the device within the joint.

In broad aspect, the size and shape of the implant are substantiallyvariable, and this variation will depend upon the joint geometry.Moreover, implants of a particular shape can be produced in a range ofsizes, so that a surgeon can select the appropriate size prior to orduring surgery, depending upon his assessment of the joint geometry ofthe patient, typically made by assessing the joint using CT, MRI,fluoroscopy, or other imaging techniques.

The rigid opposing plates or shells can be made of any rigid,biocompatible material, but are generally made of a biocompatible metal,such as stainless steel, cobalt chrome, ceramics, such as thoseincluding Al₂O₃ or Zr₂O₃, or titanium alloy. ASTM F-136 titanium alloyhas been found to be particularly suitable. As indicated above, theouter surface of the rigid opposing plates or shells are rough, in orderto restrict motion of the shells relative to the bone surfaces that arein contact with the plates. This is particularly important in the timeperiod just after implantation (the “acute” phase of healing), sinceexcessive movement of the implant relative to the bone can result in theformation of fibrous tissue between the bone and the implant, ratherthan the bony ingrowth, which is desirable for long term implantstability (i.e., during the “chronic” phase of healing). It has beendiscovered that a porous coating formed from nonspherical sintered beadsprovides very high friction between the outer surface of the shell andthe bone, as well as providing an excellent interaction with thecancellous bone of the joint, increasing the chances of bony ingrowth.One example of a suitable nonspherical sintered bead coating is thatmade of pure titanium, such as ASTM F-67. The coating can be formed byvacuum sintering.

At least a portion of the inner surface of each plate or shell issmooth, and of a shape thatcomplements and articulates with the shape ofat least a portion of the central body. This smoothness andcorrespondence in shape provides unconstrained movement of the plate orshell relative to the central body, provided that this movement occurswithin the allowable range of motion.

The structural features of the shapes of the inner surface of the plateor shell and the central body that interact to limit the movement tothis allowable range will necessarily vary to some extent, based on thejoint in which the implant will be used. As an example, the edge of theplate or shell can be extended toward the central body, so as to form awall that, under shear, can contact a ridge or shoulder formed in thesurface of the central body. This will allow for unconstrained motion ofthe plate or shell except in a direction that will bring the extensioninto contact with the ridge. By forming the extension around the entireedge of the shell, and by forming a ridge or shoulder that encloses aportion of the surface of the central body, translational, flexural,extensional, and lateral motion of the plate or shell relative to thecentral body can be constrained in all directions. Those of skill in theart will recognize that a bead or ridge at other locations on the innersurface of the plate or shell will serve a similar purpose, and that thelocation of this bead or ridge, as well as the ridge or stop on thecentral body, can be varied between implants for different joints, inorder to obtain the desired range of motion for that particular joint.

The plates may be identical, which is desirable for ease of manufacture,or may be of different design (shape, size, and/or materials) to achievedifferent mechanical results. For example, differing plate or shellsizes may be used to more closely tailor the implant to a patient'sanatomy, or to shift the center of rotation in the cephalad or caudaldirection.

In a more particular embodiment, the inner surface of the shell and theouter surface of the central body can contain complementary structuresthat will function as an expulsion stop, so that the central body cannotbe expelled from between the opposing plates or shells when the platesor shells are at maximum range of motion in flexion/extension. Examplesof such structures include a post and corresponding hole to receive thepost. The hole can have a diameter sufficiently large that relativemotion between the shells and central body is unconstrained within theallowable range of motion, but that will nevertheless cause the post toarrest the central body before it is expelled from the implant underextreme compression. Alternatively, the diameter of the post may be suchthat it limits the translational movement of the central body duringnormal motion of the spine by contacting the surface of the hole in thecentral body at the limit of the allowable range of motion for thedevice.

The elastically deformable, resilient central body may also varysomewhat in shape, size, composition, and physical properties, dependingupon the particular joint for which the implant is intended. The shapeof the central body should complement that of the inner surface of theshell to allow for a range of translational, flexural, extensional, androtational motion, and lateral bending appropriate to the particularjoint being replaced. The thickness and physical properties of thecentral body should provide for the desired degree of elasticity ordamping. Accordingly, an elastomeric material is typically used for thecentral body. However, the central body should be sufficiently stiff toeffectively cooperate with the shell surfaces to limit motion beyond theallowable range. The surface of the central body should be sufficientlyhard to provide acceptable wear characteristics. One way to achieve thiscombination of properties is to prepare a central body having surfaceregions that are harder than the material of the central body closer toits core. The central body is therefore desirably a biocompatibleelastomeric material having a hardened surface. Polyurethane-containingelastomeric copolymers, such as polycarbonate-polyurethane elastomericcopolymers and polyether-polyurethane elastomeric copolymers, generallyhaving durometer ranging from about 80A to about 65D (based upon raw,unmolded resin) have been found to be particularly suitable forvertebral applications. If desired, these materials may be coated orimpregnated with substances to increase their hardness or lubricity, orboth. Examples of suitable materials are provided in more detail below.

The shape of the central body may also be designed to prevent contactbetween the edges of the rigid opposing shells during extreme motion ofthe implant. For example, a ridge or lip in the region of the centralbody between the shells and extending laterally can provide a buffer,preventing contact between the shells. This prevents friction and wearbetween the shells, thereby avoiding the production of particulates,which could cause increased wear on the internal surfaces of theimplant.

In a particular embodiment, one or both of the rigid opposing shells canbe provided with an opening therein, in the form of a passage betweenthe outer and inner surfaces. When the implant is partially assembled,i.e., the deformable resilient central body has been disposed betweenthe rigid opposing shells, and the sheath has been attached to the edgesof the shells, the passage can be used to introduce liquid lubricantinto the implant. The passage can then be closed off (e.g., by fillingit with an appropriately sized plug), thereby providing a sealed,lubricant filled inner cavity.

Attachment of the sheath to the rigid, opposing shells can beaccomplished in a variety of ways. Typically the rigid opposing shell ismade from a biocompatible metallic alloy, e.g., a titanium alloy, whilethe sheath is typically made from an elastomeric polymeric material,such as segmented polyurethane. Attachment of the sheath to the shellcan be accomplished by providing the edge of the rigid shell with acircumferential groove (the term “circumferential” in this context doesnot imply any particular geometry). The groove is of a shape and depthsufficient to accept a retaining ring, typically made of a biocompatibleweldable wire, such as stainless steel or titanium. The sheath can bedisposed so that it overlaps the circumferential groove, and theretaining ring formed by wrapping the wire around the groove over theoverlapping portion of the sheath, cutting the wire to the appropriatesize, and welding the ends of the wire to form a ring. Laser welding hasbeen found to be particularly suitable in this regard.

The embodiment as described above can be used as a prosthetic implant ina wide variety of joints, including hips, knees, shoulders, etc. Thedescription below focuses on an embodiment wherein the implant is aspinal disc endoprosthesis, but similar principles apply to adapt theimplant for use in other joints. Those of skill in the art will readilyappreciate that the particulars of the internal geometry will likelyrequire modification from the description below to prepare an implantfor use in other joints. However, the concept of using a core bodyhaving geometric features adapted to interact with inner surfaces ofopposing shells to provide relatively unconstrained movement of therespective surfaces until the allowable range of motion has beenreached, and the concept of encasing these surfaces in a fluid filledcapsule formed by the opposing shells and a flexible sheath, areapplicable to use in any joint implant.

Reference is made below to the drawings, which shall now be used toillustrate a specific embodiment, namely a spinal disc endoprosthesis.As can be seen best in the exploded view shown in FIG. 7, in accordancewith this preferred embodiment, the implant includes four maincomponents: two shells 20, 40, a central body 60, and a sheath 70. Thecomplete assembly of the device is shown in FIGS. 4 and 6, wherein thecentral body 60 is bracketed between shells 20, 40. The flexible sheath70 extends between the two opposing shells 20, 40, and encapsulates thecentral body 60. As described in further detail below, the geometricconfiguration of the shells 20, 40, the central body 60, and the sheath70, are complementary. As such the geometric configuration of thesecomponents cooperate to (1) join the components into a unitarystructure, and (2) define important functional features of the device.

Preferably, shells 20, 40 are cup-like so as to include an outer convexsurface 23 and an inner concave surface 21, 41. The outer surfaces 23can be coated with a nonspherical sintered bead coating 22, 42, or withsome other coating that will promote bony ingrowth. The inner surfaces21, 41 (shown in FIG. 6) are preferably very smooth, and may be machinedor polished.

The shells 20, 40 include a number of geometric features that asdescribed in further detail below cooperate with other components of thedevices. Specifically, these features include a central retaining post27, 47, an outer circumferential groove 82, 84, and a radial stop or anextension 86, 88. The central retaining post 27, 47 extends axially frominner surfaces 21, 41. In addition, each shell 20, 40 includes an edge73, 74, respectively. The outer circumferential grooves 82, 84 extendinto the edges 73, 74 of the shells 20, 40. As seen best in FIG. 6, theradial stops or extensions 86, 88 extend from the edges 73, 74 in adirection generally perpendicular to the general plane of the shells 20,40.

Each shell 20, 40 may also be provided with tabs or flanges 25, 45. Thetabs or flanges 25, 45 extend from a portion of the edges 73, 74 in adirection generally perpendicular to the general plane of the shells 20,40, but in a direction generally opposite the radial stops or extensions86, 88. The tabs or flanges 25, 45 help to prevent long-term migrationwithin the disc space, as well as catastrophic posterior expulsion, andthe resulting damage to the spinal cord, other nerves, or vascularstructures. The tabs or flanges 25, 45 may contain openings 26, 46 thatcan releasably engage an insertion tool (not shown). The insertion toolwill generally contain flexible prongs to releasably engage openings 26,46. The insertion tool will also generally include a disengagement blockthat can press against the side of the implant once it has been properlypositioned in the intervertebral space and force the openings 26, 46 offof the prongs of the tool. The shells 20, 40 can be made from anysuitable biocompatible rigid material. In accordance with a preferredembodiment, the shells 20, 40 are made from a titanium alloy, and mostpreferably the titanium alloy is ASTM F-136. The bead coating 22, 42,however, is preferably made from ASTM F-67 pure titanium.

As shown best in FIG. 7, central body 60 is preferably a donut-shapedstructure, and includes a convex upper contact surface 94, a convexlower contact surface 96, and a central axial opening 98 formed throughan inner surface 67 of the central body. In addition, central bodymember 60 preferably includes an upper shoulder 92 and a lower shoulder90. Each shoulder 90, 92 consists of an indentation in the surface ofthe central body member which defines a ledge that extends around thecircumference of the central body 60.

The central body 60 is both deformable and resilient, and is composed ofa material that has surface regions that are harder than the interiorregion. This allows the central body to be sufficiently deformable andresilient that the implant functions effectively to provide resistanceto compression and to provide dampening, while still providing adequatesurface durability and wear resistance. In addition, the material of thecentral body has surfaces that are very lubricious, in order to decreasefriction between the central body and the rigid opposing shells.

The material used to make the central body is typically a slightlyelastomeric biocompatible polymeric material, which may be coated orimpregnated to increase surface hardness, or lubricity, or both, asdescribed above. Coating may be done by any suitable technique, such asdip coating, and the coating solution may include one or more polymers,including those described below for the central body. The coatingpolymer may be the same as or different from the polymer used to formthe central body, and may have a different durometer from that used inthe central body. Typical coating thickness is greater than about 1 mil,more particularly from about 2 mil to about 5 mil. Examples of suitablematerials include polyurethanes, such as polycarbonates and polyethers,such as Chronothane P 75A or P 55D (P-eth-PU aromatic, CT Biomaterials);Chronoflex C 55D, C 65D, C 80A, or C 93A (PC-PU aromatic, CTBiomaterials); Elast-Eon II 80A (Si-PU aromatic, Elastomedic); Bionate55D/S or 80A-80A/S (PC-PU aromatic with S-SME, PTG); CarboSil-10 90A(PC-Si-PU aromatic, PTG); Tecothane TT-1055D or TT-1065D (P-eth-PUaromatic, Thermedics); Tecoflex EG-93A (P-eth-PU aliphatic, Thermedics);and Carbothane PC 3585A or PC 3555D (PC-PU aliphatic, Thermedics).

The last main component of this embodiment is the sheath 70. As show inFIG. 7, the sheath 70 is a tubular structure, and is made from aflexible material. The material used to make the sheath is typicallybiocompatible and elastic, such as a segmented polyurethane, having athickness ranging from about 5 to about 30 mils, more particularly about10-11 mils. Examples of suitable materials include BIOSPAN-S (aromaticpolyetherurethaneurea with surface modified end groups, PolymerTechnology Group), CHRONOFLEX AR/LT (aromatic polycarbonate polyurethanewith low-tack properties, CardioTech International), CHRONOTHANE B(aromatic polyether polyurethane, CardioTech International), CARBOTHANEPC (aliphatic polycarbonate polyurethane, Thermedics).

As noted above, the various geometric features of the main components ofthis embodiment cooperate to join the components into a unitarystructure. In general, the ends of the sheath 70 are attached to theshells, and the central body 60 is encapsulated between the shells 20,40 and the sheath 70. More specifically, referring to FIG. 6, preferablythe edges of flexible sheath 70 can overlap the outer circumferentialgrooves 82, 84 of the shells 20, 40. Retaining rings 71, 72 are thenplaced over the edges of the sheath 70 and into the circumferentialgrooves 82, 84, thereby holding the flexible sheath in place andattaching it to the shells. While any suitable biocompatible materialcan be used for the retaining rings, titanium or titanium alloys havebeen found to be particularly suitable. The retaining rings aredesirably fixed in place by, e.g., welding the areas of overlap betweenthe ends of the retaining rings. Because of the high temperatures neededto weld titanium and titanium alloys, and because of the proximity ofthe weld area to both the flexible sheath 70 and the central body 60,laser welding is typically used.

As also noted above, the various geometric features of the maincomponents of this embodiment cooperate to define important functionalfeatures of the device. These features primarily include defining thekinematics of motion provided by the device, prohibiting expulsion ofthe central body 60, providing post assembly access to the interior ofthe device, providing an attachment mechanism for inserting the device,and providing a port for the insertion of lubricant into the implantcavity.

The kinematics of the motion provided by the prosthesis are definedprimarily by the geometric interaction of the central body 60 and theshells 20, 40. Although the central body is encapsulated within thesheath and the shells, it is not attached to these components.Accordingly, the central body 60 freely moves within enclosed structureand is only constrained by geometric limitations. As seen best in FIG.6, the concave shape of the inner surfaces 21, 41 of shells 20, 40complements the convex surfaces 94, 96 of central body 60. As the shells20, 40 glide across the convex surfaces 94, 96, relatively unconstrainedtranslational, flexural, or extensional motion of shells 20, 40 withrespect to central body 60 is achieved. When the desired limit of therange of motion is reached, extensions 86, 88 on shells 20, 40 aredesigned to contact shoulders 90, 92 on the central body 60.Specifically, the inner portion of the extension forms a circumferentialridge that limits the range of motion of the shells 20, 40 relative tothe central body 60 by contacting central body shoulders 90, 92 at theend of the allowable range of motion. In an actual vertebral joint, thisoccurs at a joint flexion/extension of about ±10°, at lateral bending ofabout 11°, and/or at translation of about 2-3 mm.

As explained above, in one embodiment, the shells are concavo-convex,and their inner surfaces mated and articulated with a convex outersurface of the deformable resilient central body. The implant alsocontains a sheath or sleeve that is secured to the rims of the shellswith retaining rings, and which, together with the inner surfaces of theshells, forms an implant cavity. In a particular aspect of thisembodiment, using a coordinate system wherein the geometrical center ofthe implant is located at the origin, and assigning the x-axis to theanterior (positive) and posterior (negative) aspect of the implant, they-axis to the right (positive) and left (negative) aspect of theimplant, and the z-axis to the cephalad (positive) and caudal (negative)aspects of the implant, the convex portion of the outer surface and theconcave portion of the inner surface of the shells can be described as aquadric surfaces, such that${\frac{x^{2}}{a^{2}} + \frac{y^{2}}{b^{2}} + \frac{z^{2}}{c^{2}}} = 1$

where (±a,0,0), (0,±0), and (0,0,±c) represent the x, y, and zintercepts of the surfaces, respectively. Typical magnitudes for a, b,and c are about 11 mm, 30 mm, and 10 mm, respectively.

The implant is symmetrical about the x-y plane, and is intended to beimplanted in the right-left center of the disc space, but may or may notbe centered in the anterior-posterior direction. In any event, theimplant is not allowed to protrude in the posterior direction past theposterior margin of the vertebral body.

As noted above, geometric features also serve to prevent the expulsionof the central body 60. In particular, this is achieved by the geometricinteraction of the shells 20, 40 and the central body 60. Shells 20, 40also contain central retaining posts 27, 47 which extend axially frominner surfaces 21, 41 into a central axial opening 98 in central body 60and which stop central body 60 from being expelled from the implantduring extreme flexion or extension. The diameter of central axialopening 98 is somewhat larger than the diameter of central retainingposts 27, 47. In the coordinate system described above, the central axisof the retaining posts 27, 47 is typically coincident with the z-axis,but may move slightly to accommodate various clinical scenarios. Theshape of the posts 27, 47 may be any quadric surface. However, atruncated tapered elliptical cone is a particularly suitable geometry.Similarly, the geometry of the central axial opening 98 of the centralbody 60 will correspond to the geometry of the retaining posts 27, 47,and will have a similar geometry.

Also described above, the shells 20, 40 contain extensions or walls 86,88 formed on the inner surface 21, 41, for example around the edge ofthe shell, and that extend toward the deformable resilient central body60. This extension or wall 86, 88 limits allowable translation of thedeformable resilient central body 60 with respect to the shell when theextension comes into contact with the shoulder 90, 92 formed on thesurface of the central body, e.g., under shear loading of the implant.The height of the extension or wall 86, 88 should be less than about 2.5mm in order to allow the full range of desired flexion/extension andright/left lateral bending motions.

The resilient deformable central body 60 contains surfaces that aredescribed by an equation similar to that for the inner surfaces 21, 41of the shells, and which articulates with those inner surfaces. Thecentral body 60 will have a plane of symmetry if identical opposingshells 20, 40 are used. As described above, the central body 60 alsofeatures an equatorial ridge 99 that acts as a “soft stop” in the eventthe patient participates in extreme activities that result in movementsgreater than the designed range of flexion/extension or lateral bending.In such a situation, the central body 60 will have translated until theretaining post 27, 47 has contacted the inner surface of the centralaxial opening 98, and the extension or wall 86, 88 will have contactedthe shoulder of the central body. Opposite the wall/shoulder contact,the edges of the shells will be in close proximity, but will be keptfrom contacting each other by contact with the equatorial ridge 99 ofthe central body. If desired, the thickness of the ridge 99 can bevaried to further limit the range of motion.

Another important characteristic of this embodiment is the provision ofa means for accessing the interior of the device after it has beenassembled into a unitary structure. This means consists of a centralaxial opening included in the shells 20, 40. Typically, this openingwill be provided through central retaining posts 27, 47. By providingaccess to the interior of the device, sterilization can be done justprior to implantation of the device. Sterilization is preferablyaccomplished by introducing an ethylene oxide surface sterilant. Cautionshould be exercised in using irradiation sterilization, as this canresult in degradation of the polymeric materials in the sheath 70 orcentral body 60, particularly if these include polyurethanes.

After sterilization, the central openings can be sealed using plugs 28,48. Preferably, only one plug is inserted first. The plug is insertedusing insertion tool 100, shown in FIG. 5, and which contains handle 101and detachable integral plug 28, 48. The tool 100 is designed so thatplug 28, 48 detaches from the tool when a predetermined torque has beenreached during insertion of the plug. The tool 100 can then bediscarded.

After one plug has been inserted into one of the shells, a lubricant 80is preferably introduced into the interior of the device prior toinserting the second plug. To do this a syringe is used to introduce thelubricant into the remaining central opening, and the implant isslightly compressed to remove some of the excess air. Another insertiontool 100 is then used to insert a plug into that central opening,thereby completely sealing the interior of the device from its exteriorenvironment. In accordance with one embodiment the lubricant 80 issaline. However, other lubricants may be used, for example, hyaluronicacid, mineral oil, and the like.

The two shells 20, 40 are virtually identical in shape and composition,however those of skill in the art will understand that it is possible touse shells of different sizes (including thicknesses), shapes, ormaterials, e.g., in order to provide a more customized fit to thepatient's anatomy.

The deformable resilient central body 60 is disposed between the opposedshells, as described above and illustrated in the drawing figures. Itsupper and lower surfaces articulate with the upper and lower shells,respectively, and have a geometry that is similar to that of the shells.

The kinematics of various embodiments of the implant are illustrated inFIG. 8, 9, 10, and 11. FIG. 8A illustrates a plan view of an implanthaving a hollow central retaining post and undergoing lateral bending.The range of lateral bending is limited to about 11°, such as in FIG.8B, which is a sectional view along line 8B-8B of FIG. 8A. Contact ofthe walls or extensions 86, 88 of the shells with shoulders 90, 92 ofthe central body limit the range of motion to that desired. The centralretaining posts 27, 47 may also contribute to limiting the range ofmotion by contact with the central axial opening 98 of the central body.FIG. 9A illustrates a plan view of an implant of the type shown in FIG.8 undergoing lateral translation. FIG. 9B shows a sectional view alongline 9B-9B. Again, the contact between walls or extensions 86, 88 of theshells and shoulders 90, 92 of the central body limit the range ofmotion to that desired, and central retaining posts 27, 47 may alsocontribute to limiting the range of motion. FIGS. 10 and 11 providesimilar plan and sectional views (along line 10B-10B and 11B-11B,respectively), illustrating a different embodiment of the implant(without a hollow central retaining post) undergoing lateral bending(FIG. 10) and lateral translation (FIG. 11). In each case, the range ofmotion is limited by contact between walls or extensions 86, 88 of theshells and shoulders 90, 92 of the central body.

As described above, the implant is desirably used as an endoprosthesisinserted between two adjacent vertebral bodies. The implant may beintroduced using a posterior or anterior approach. For cervicalimplantation, an anterior approach is preferred. The implantingprocedure is carried out after discectomy, as an alternative to spinalfusion. The appropriate size of the implant for a particular patient,determination of the appropriate location of the implant in theintervertebral space, and implantation are all desirably accomplishedusing precision stereotactic techniques, apparatus, and procedures, suchas the techniques and procedures described in copending U.S. Ser. No.09/923,891, filed on Aug. 7, 2001, the entire contents of which arehereby incorporated by reference. Of course, non-stereotactic techniquescan also be used. In either case, discectomy is used to removedegenerated, diseased disc material and to provide access to theintervertebral space. This access is used to remove a portion of thevertebral body using a burr or other appropriate instruments, in orderto provide access to the intervertebral space for a transverse millingdevice of the type described in U.S. Ser. No. 08/944,234, the entirecontents of which are hereby incorporated by reference. The millingdevice is used to mill the surfaces of the superior and inferiorvertebral bodies that partially define the intervertebral space tocreate an insertion cavity having surfaces that (a) complement the outersurfaces of the implant and (b) contain exposed cancellous bone. Thisprovides for an appropriate fit of the implant with limited motionduring the acute phase of implantation, thereby limiting the opportunityfor fibrous tissue formation, and increases the likelihood for bonyingrowth, thereby increasing long-term stability.

Referring now to FIG. 12, an alternative embodiment of a human jointprosthesis 102 is provided. Prosthesis 102 is particularly adapted forreplacing a spinal disc, and in particular a lumbar spinal disc.Prosthesis 102 includes an upper member 104, a lower member 106, and acentral member 108. The upper member 104 and lower member 106 mayinclude an anterior wing 110, as illustrated in FIG. 12. Alternatively,the anterior wings may be excluded from the device. If an anterior wingis included, it may include anterior wing opening 112 to facilitateattaching the device to an insertion or removal tool. The upper member104 and lower member 106 may also include a circumferential groove 114.Circumferential groove 114 is adapted to receive a retaining ring (notshown) which would secure a sheath (not shown) to the upper and lowermembers as shown in the embodiment illustrated in FIG. 1.

The upper and lower members 104, 106 preferably include an outer surfacehaving a posterior stabilizing flat 116, an anterior stabilizing flat118, and an outer surface 120 extending therebetween. As is described ingreater detail herein below, posterior stabilizing flat 116 and anteriorstabilizing flat 118 provide a means for preventing rotation of thedevice about its anterior-posterior axis. In addition, upper and lowermembers 104, 106 many also include interior access port 122. Interioraccess port 122 provides a means for introducing a lubricant into theinterior of the device.

FIG. 13 provides a schematic perspective view of the implantedendoprosthesis with one of the vertebral bodies cut away to show thearrangement of the endoprosthesis with the remaining vertebral body 126.As shown, the endoprosthesis 102 is implanted such that anterior wing110 adjoins the anterior surface of the vertebral body.

FIG. 14 is a side perspective view of the implanted endoprosthesiscorresponding to FIG. 13. The anterior-posterior angulation of theendoprosthesis in its prepared cavity relative to the surface of thevertebral body endplate is apparent.

FIG. 15 is a front schematic view of the implanted endoprosthesis withone of the vertebral bodies cut away.

FIG. 16 and FIG. 17 are top schematic views of two embodiments of animplanted endoprotheses. As is apparent, the lateral profile of theupper and lower members of these embodiments are slightly different; theembodiment shown in FIG. 16 has a more rectilinear profile, while theembodiment shown in FIG. 17 has a more curvilinear profile. The lateralprofile of the disc space prepared to receive each of these embodimentswill therefore be correspondingly different, and may require a differentprofile of bone removal tool.

FIG. 18 provides an anterior-posterior cross-sectional schematic view ofthe device implanted between two vertebral bodies—the cephalad vertebralbody 124 and the caudal vertebral body 126. As illustrated in FIG. 18,upper and lower members 104, 106 each include an upper centering post128 and central member 108 includes a lower central opening 130. Inaccordance with this embodiment, access port 122 (shown in FIG. 12)extends through the centering post 128. Each of the upper and lowermembers 104, 106 also include an interior articulating surface 132 thatmoves over the corresponding outer surface of central member 108. Inaccordance with a particular embodiment, articulating surface 132 and/orthe corresponding outer surface 120 of central member 108 are arcuatesurfaces. The arcuate surfaces may be essentially conical, spherical orelliptical sections in nature. In addition, the interior articulatingsurface 132 within the upper member may be the same as, or differentfrom, the interior articulating surface 132 within the lower member. Ifthis is the case, the corresponding outer surface 120 of central member108 will vary on either side thereof.

As also illustrated in FIG. 18, the caudal-cephalad thickness of upperand lower members 104, 106 may vary along the anterior-posterior axis ofthe device. In particular, upper and lower members 104, 106 include anenlarged anterior portion 134 and a thinner posterior portion 136. Therelative thickness of posterior portion 136 of upper and lower members104, 106 as compared to anterior portion 134 can be adjusted to vary thelordotic angle imposed on the vertebrae by the device. In accordancewith a preferred embodiment, the caudal-cephalad height of the anteriorportion of the device is greater than the caudal-cephalad height of theposterior portion of the device when the device is in its neutralposition, i.e. the mid-point between its full flexion and extensionrange of motion. In accordance with an alternative embodiment, therelative height of the anterior and posterior portions of the uppershell may be the same as or different from the relative height of theanterior and posterior portions of the lower shell.

Referring now to FIG. 19, unique surgical instrumentation used toimplant an endoprosthesis is provided. This instrumentation isparticularly useful for preparing the vertebral disc space to receivethe prostheses 102. FIG. 19A illustrates a bone removal device 140mounted within a support frame 138 that is attached to vertebral bodies124 and 126.

Support frame 138 consists of a base 164 and two angled guide tracks152. In accordance with the embodiment illustrated in FIG. 19A, an uppersupport member 168 links the proximal ends of the two tracks 152, andenhances the rigidity of support frame 138. Base 164 is attached to thedistal end of guide tracts 152, and is adapted to be attached tovertebral bodies 124, 126. In addition, base 164 may include a pluralityof adjustable bushings 166 for receiving a locking mechanism, such asfor example an anchor post and an anchor post nut, which locks orsecures the position of the support frame 138 to the vertebral bodies.

Each angled guide track 152 extends from base 164 at an angle relativeto base 164. This angle can be used to set the angle at which the boneremoval tool will be introduced into the intervertebral disc space. Inaccordance with a preferred embodiment for use in the lumbar spine, theangle of track 152 relative to base 164 is between 0 degrees and 90degrees. Track 152 may include a hinge that permits the user to set theangle of track 152 relative to base 164.

A position control mechanism 154 is associated with each track 152.Position control mechanism 154 includes a threaded rod 156 having aproximal end 158 and a distal end 160. Proximal end 158 includes anactuating knob 174. Distal end 160 includes a threaded segment that mayor may not extend completely to the tip of distal end 160. Positioncontrol mechanism further includes a position plate 162. Position plate162 includes a threaded opening for receiving the threaded portion ofposition control mechanism 154. Position plate 162 is attached to guidetrack 152. Desirably, position plate 162 is slideably attached to guidetrack 152 so that the location of position plate 162 along the length ofguide track 152 may be varied.

A position guide block 142 is also associated with each track 152 and isshown in more detail in FIG. 19B. Position block 142 includes an axialopening 144, an axial slot 146, a pivot slot 148 (FIG. 19A), and alocking mechanism 150. Axial slot 146 is adapted to receive track 152,and enables position guide block to slide along track 152. Axial opening144 is adapted to receive bone removal tool 140. Bone removal tool 140includes distal and proximal pivot pins (not shown). When bone removaltool 140 is inserted into opening 144, distal and proximal pivot pins onthe bone removal tool are positioned within and travel along a pivot pinslot (not shown) of position guide block 142. In accordance with apreferred embodiment, bone removal tool 140 is properly positionedwithin position guide block 142 when its distal pivot pin is positionedat the distal end of pivot pin slot 149 and its proximal pivot pin isaligned with pivot slot 148 of position guide block 142.

The locking mechanism 150 of position guide block 142 locks the positionguide block to the position plate 162 of position control mechanism 154.In accordance with the embodiment illustrated in FIG. 19A, lockingmechanism 150 includes a threaded screw 170 that passes through an axiallocking mechanism opening 172 (FIG. 19B) within position guide block142. The distal end of threaded screw is threaded into a threadedopening in position plate 162, thereby securely attaching position guideblock 142 to position plate 162.

In use, support frame 138 is properly positioned over the target discspace and securely attached to the vertebral bodies, and preferablyattached to an anterior surface the vertebral bodies. Support frame 138may be properly positioned using the method and techniques described forpositioning a machining jig or scaffold in U.S. patent application Ser.No. 09/923,891, filed on Aug. 7, 2001 entitled “Method and Apparatus forStereotactic Implantation,” the entire contents of which is incorporatedherein by reference. Position guide block 142 is positioned along one ofthe tracks 152, and locking mechanism 150 is used to secure positionguide block 142 to position plate 162. Bone removal device 140 is thenproperly positioned with position guide block 142 in the mannerdescribed hereinabove. Bone removal device 140 is then pivoted withinposition guide block 142 such that its proximal pivot pin (or pins)travels back and forth to the ends of pivot slot 148. While pivotingbone removal device 140, the user rotates actuating knob 174 of positioncontrol mechanism 154, thereby lowering (i.e., moving toward thevertebral bodies) position plate 162 relative to threaded rod 156. Thisalso lowers position guide block 142, which has been locked to positionplate 162 by locking mechanism 150, and thus lowers the bone removalelement (not shown in FIG. 19) of bone removal device 140 into theintervertebral disc space.

Bone removal device 140 may be of the type described in co-pending U.S.patent application Ser. No. 09/934,507, filed on Aug. 22, 2001, which isincorporated herein by reference. Alternatively, bone removal device 140may be of the type illustrated in FIG. 20. In accordance with theembodiment illustrated in FIG. 20, bone removal device 140 includes abone removal handpiece 176 and a bone removal instrument 178. Boneremoval instrument 178 includes a shaft 182 and a bone removal element184. In accordance with a preferred embodiment, bone removal element 184consists of a cutting element and may include a plurality of cuttingflutes or cutting edges 186. Bone removal handpiece 176 includes a driveconnecting portion 187 positioned at its proximal end, and a hollowchannel 180 extending along its length. Shaft 182 is positioned withinhollow channel 180, and extends from drive connecting portion 187 ofhandpiece 176. In use, handpiece 176 is attached to a power source (notshown) via drive connecting portion 187. The power source may be anyconventional power source such as an electric or air-powered motor.Handpiece 176 also includes positioning portion 188 that has proximalpin or stop 190 and distal pin 192.

FIG. 21 illustrates the cross sectional profile of a bone removalinstrument 200. In accordance with this embodiment, bone removal element184 is connected to shaft 182, and includes a distal bone removalsection 194, a central bone removal section 196, and a proximal boneremoval section 198. In the embodiment illustrated, distal and proximalbone removal sections 194, 198 are substantially rectilinear, andcentral bone removal section 196 is substantially curvilinear orarcuate.

As illustrated in FIG. 22, bone removal instrument 200 may be used tocreate a profile 202 within an endplate of a vertebral body that matchesthe profile of prosthesis 102 shown in FIG. 12. In particular, boneremoval instrument 200 may be inserted into handpiece 176 to form boneremoval device 140 that may be inserted into axial opening 144 ofposition guide block 142 in the manner describe above with reference toFIG. 19. Referring again to FIG. 22, as the bone removal device ispivoted within guide block 142, proximal bone removal section 198 willform an anterior surface 204 complementary to anterior stabilizing flat118, distal bone removal section 194 will form a posterior surface 206complementary to posterior stabilizing flat 116, and central boneremoval section 196 will form a central surface 208 that iscomplementary to outer surface 120 of prosthesis 102.

Those skilled in the art will appreciate that although the stabilizingflats and their complementary surfaces formed in the endplate arerectilinear in anterior-posterior direction, they will be curvilinear orarcuate in the lateral direction because of the pivoting motion of thebone removal device as it is manipulated to remove bone from theendplates. Alternatively, a lateral translation mechanism may beincluded as part of or to interface with one or some combination of theposition guide block, the support frame, and/or the handpiece, whichwould enable the bone removal element to translate laterally along theendplate and create a substantially rectilinear surface in the lateraldirection for a prosthesis having laterally linear stabilizing flats.

In accordance with a preferred technique, endplate profile 202 iscreated by multiple lateral passes of bone removal element 200 as itscaudal-cephalad position is changed. In particular, a caudal-cephaladtranslation mechanism may be included as part of or to interface withone or some combination of the position guide block, the support frame,and/or the handpiece, which would enable the bone removal element totranslate in the caudal-cephalad direction.

FIGS. 23-37 illustrate instrumentation which may be used to createendplate profile 202.

FIG. 23 shows a distal end of a sagittal wedge 300, which includes discspace penetrating portion 302, shoulder 304, and shaft 308. The proximalend 306 of disc penetrating portion 302 is preferably curved toapproximate the profile of the anterior surface of the vertebral bodiesbetween which it is inserted. Sagittal wedge 300 is used in the samemanner as the sagittal wedge is used in the method described in U.S.application Ser. No. 09/923,891, filed on Aug. 7, 2001 entitled “Methodand Apparatus for Stereotactic Implantation”.

As illustrated in FIG. 24, when sagittal wedge 300 is properly seatedsuch that shoulder 304 rests on the anterior surfaces of the adjacentvertebral bodies, the posterior tip of disc penetrating portion 302 ispositioned at approximately the anterior-posterior midpoint of the discspace. In accordance with a preferred embodiment, the anterior-posteriorlength of disc penetrating portion 302 is between approximately 12 mmand approximately 18 mm. In addition, the lateral dimension of discpenetrating portion 302 is up to 24 mm. As shown in FIG. 24, the lateraldimension of shoulder 304 is less than the lateral dimension of discpenetrating portion 302, which enhances the surgeon ability to view theinterior of the disc space during surgery.

FIG. 25 and FIG. 26 show a support frame 318, which includes lateralsupport members 312, base 310, and upper support member 342. In use,support frame 318 is positioned over sagittal wedge 300 (as illustratedin FIG. 26) in the same manner that the scaffold is placed over thesagittal wedge in U.S. application Ser. No. 09/923,891, filed on Aug. 7,2001 entitled “Method and Apparatus for Stereotactic Implantation”.Support frame 318 also serves a similar purpose as the scaffold, in thatit is used to properly position instruments relative to a targetintervertebral disc space.

As shown in FIG. 25, base 310 includes one or a plurality of openings314 adapted to receive a retaining pin 332 (shown in FIG. 28) thataffixes support frame 318 to the anterior surfaces of the adjacentvertebral bodies. In addition, base 310 and/or its posterior surface 316may be curved to approximate the profile of the anterior surface of thevertebral bodies. Such a curved profile enhances the surgeon's abilityto stabilize the frame's position relative to the vertebral bodies, andmay improve the surgeon's field of view of the intervertebral discspace. Base 310 of support frame 318 contains a large central openingsufficient to accommodate placement of the support frame over sagittalwedge 300, and to allow introduction and manipulation of bone removalelement 184 of bone removal device 140.

A disc spacer clip 320 is shown in FIG. 27, which includes upper members322 and lower members 324. As shown in FIG. 28, clip 320 is positionedover sagittal wedge 300 after frame 318 is placed over wedge 300. Discspacer clip 320 is positioned such that lower members 324 extend intothe disc space on opposite sides of disc penetrating portion 302 ofsagittal wedge 300, and upper members 322 rest on the anterior surfacesof the vertebral bodies. Upper members 322 may include at least onekeyway 328 that is adapted to receive shoulder 304 of sagittal wedge300. Upper members 322 may also include support frame interface 330,which may include an opening to enable a fixation device to securelyattach disc spacer clip 320 to frame 318. As described in greater detailbelow, lower members 324 define a pivot saddle 326 that provides a pivotpoint for instruments inserted into the disc space. Disc spacer clip 320is sized and shaped to fit within the resected annulus. Once thesagittal wedge 300 is removed, disc spacer clip 320 helps to maintainposterior distraction within the disc space.

After disc spacer clip 320 is properly positioned, support frame 318 ispositioned (e.g., in the same manner the aforementioned scaffold ispositioned as described in U.S. application Ser. No. 09/923,891, filedon Aug. 7, 2001 entitled “Method and Apparatus for StereotacticImplantation”), and its position is secured with one or more securingpins 332 shown in FIG. 28. Securing pin 332 includes a bone engager 334,shoulder 336, and shaft 338. Preferably, the bone engager 334 includes athreaded portion, and shaft 338 is flexible. Once the position ofsupport frame 318 is secured, sagittal wedge 300 is removed, leavingonly disc spacer clip 320, support frame 318 and securing pins 332, asshown in FIG. 29 (pins not shown).

Frame 318 may also include a connector for attaching the device to abrace similar to the scaffold brace described in U.S. application Ser.No. 09/923,891, filed on Aug. 7, 2001 entitled “Method and Apparatus forStereotactic Implantation” as shown in FIG. 29, this connector mayinclude an opening 340 adapted to receive a pin associated with thebrace.

Tilting guide member 344, which is shown in FIG. 30, is then positionedrelative to the assembly of support frame 318 and disc spacer clip 320in the manner shown in FIG. 31. Tilting guide member 344 has a distalend 346 that includes a saddle point 348, a proximal end 350 having anangle positioning and locking mechanism 352, and a mounting member 358interconnecting distal end 346 and proximal end 350. Angle positioningand locking mechanism 352 includes an arcuate track 354 having a frameattachment member 356 slideably mounted therein. Mounting member 358 mayconsist of a T-track or other mechanism to facilitate slideableattachment of other instruments to tilting guide member 344. As shown inFIG. 31, tilting guide member 344 is positioned relative to the assemblyof support frame 318 and disc spacer clip 320 such that the saddle point348 is positioned in pivot saddle 326, and frame attachment member 356is attached to the lateral support member 312 of support frame 318.Tilting guide member 344 may also include a threaded carrier 360 tocontrol the movement along mounting member 358 of instruments positionedthereon.

This design facilitates easy and quick removal of the resulting assemblyfrom the disc space, which is important to allow a surgeon to quicklyaddress any surgical complications that might occur, such as vascularbleeding. The openness of the design also allows for maximum view of thesurgical site. In addition, this design places the angle pivot point ofmounting member 358 within the disc space. This limits the need toconsider caudal-cephalad translation within the disc space in order toachieve larger angles of the instruments relative to the disc endplates.Consequently, this design is particularly useful for practicing themethods described in U.S. application Ser. No. 09/923,891, filed on Aug.7, 2001 entitled “Method and Apparatus for Stereotactic Implantation”regarding angled milling relative to the disc space and/or the discendplates.

Transverse unit 362 is shown in FIG. 32, and is adapted to be mounted onmounting member 358 of tilting guide member 344. The transverse unit 362allows the bone removal device 200 to be reliably and adjustablytranslated toward the endplates of the vertebral bodies, and thus allowsprecise control over the amount of bone removed by the bone removaldevice 200. After the bone removal device 200 is translated to contactthe endplate, it is swept laterally to remove a desired layer of tissue.The bone removal device can then be translated toward the endplate againand again swept laterally, in order to remove additional layers ofmaterial. As shown in FIG. 32A, transverse unit 362 includes a proximaltransverse block 364 and a distal transverse block 366 interconnected bytwo lateral supports 368. Each transverse block includes an outer member370, an inner member 372, and a central member 374 (shown more clearlyin FIG. 32B). Inner member 372 includes two angled slots 376 and twoopposing handpiece pivot slots 378. Outer member 370 includes twoopposing slots 380, and a mounting slot 392. Mounting slot 392 isadapted to mount transverse unit 362 onto mounting member 358 (shownmore clearly in FIG. 33). Central member 374 includes pins 382 thatextend into angled slots 376 and outer member slots 380. As seen best inFIG. 32A, central member 374 of the proximal and distal transverseblocks are different. In particular, proximal transverse block 364includes a handpiece opening 386 that is larger than handpiece opening388 in distal transverse block 366.

Transverse unit 362 further includes an actuating member 384 that linksthe central members 374 of the proximal transverse block 364 and thedistal transverse block 366. Preferably, actuating member 384 is a rodthat threadably engages the central components of the proximal anddistal transverse blocks, and includes actuating knob 394 (visible inFIG. 34). As actuating knob 394 is rotated, central members 374 arepulled closer together and pins 382 travel along angled slot 376 therebycausing inner member 372 to translate in the direction of arrow 390(shown in FIG. 33), which causes any instrument mounted on transverseunit 362 to translate toward or away from the corresponding vertebralendplate.

Referring now to FIG. 35-37, bone removal device 140 is positionedwithin the proximal and distal handpiece openings 386, 388 of transverseunit 362 such that distal pin 192 is seated in handpiece pivot slot 378of inner member 372 of proximal transverse block 364. Bone removaldevice is pivoted about pin 192 to move it laterally with respect to thevertebral endplate and translated toward or away from the vertebralendplate by turning actuating knob 394 (visible in FIG. 34) in order toguide the bone removal element (not shown) along a predetermined path tocreate a predetermined profile in the vertebral endplate. Thatpredetermined profile substantially compliments the outer profile ofintervertebral disc prosthesis 102. The oblong configuration of thedistal handpiece opening 388 serves to guide and control the path of thecutting element, as shown in FIG. 36.

As shown in FIG. 37, a pivoting tool 396 may be used to pivot boneremoval device 140. Pivot tool 396 includes a slot 398 adapted tocapture the shaft of bone removal device 140. Pivot tool 396 may beinserted into the disc space such that slot 398 captures the shaft ofdevice 140 near the distal transverse block 366. This enables thesurgeon to better control the pivot motion of the bone removal device140.

Once sufficient tissue has been removed by the bone removal device toaccommodate the intervertebral endoprosthesis on one side of the discspace (using irrigation and suction to cool the bone and remove debrisas described in U.S. application Ser. No. 09/923,891, filed on Aug. 7,2001 entitled “Method and Apparatus for Stereotactic Implantation”), theprocedure is repeated on the other side of the disc space by removingtissue from the opposing vertebral body. Once the disc space has beenprepared, the transverse unit and/or tilting guide member may beremoved, and the intervertebral endoprosthesis inserted into theprepared disc space, as described in U.S. application Ser. No.09/923,891, filed on Aug. 7, 2001 entitled “Method and Apparatus forStereotactic Implantation.”

When the intervertebral endoprosthesis is being implanted betweenvertebral bodies in the lumbar region, it may be desirable to burr atleast a portion of the anterior surfaces of the vertebral bodiessufficiently that wings 110 of the endoprosthesis 102 are partially orcompletely below the anterior surfaces of the vertebral bodies, so as toavoid contact between the wings 110 and any anatomical structures suchas vessels or nerves in the lumbar region.

Two additional embodiments of intervertebral endoprostheses, suitablefor implantation in the lumbar region, are shown in FIG. 38A and FIG.38B.

The invention has been described above with respect to certain specificembodiments thereof. Those of skill in the art will understand thatvariations from these specific embodiments are within the spirit of theinvention.

1. An assembly for preparing a vertebral disc space to receive a prosthesis, the assembly comprising: a support frame having a base and a pair of guide tracks extending from the base wherein the base is adapted to attach to a plurality of vertebral bodies; a guide block operatively connected to at least one of the guide tracks, the guide block having an opening disposed there through; a position control mechanism corresponding to the at least one of the guide tracks, the position control mechanism having a plate extending there from for coupling to the guide track and the guide block and an actuating knob for adjusting the position of the plate and therefore the guide block; and a bone-removal device positioned through the opening of the guide block and operatively connected to the guide block.
 2. The assembly of claim 1 further comprising an upper support member for linking the proximal ends of the guide tracks.
 3. The assembly of claim 1 further comprising a plurality of adjustable bushings for receiving a locking mechanism for securing the support frame to the vertebral bodies.
 4. The assembly of claim 1 wherein the guide tracks angle outwards relative to the base.
 5. The assembly of claim 4 wherein each of the guide tracks includes a hinge for setting the angle of the guide tracks relative to the base.
 6. The assembly of claim 1 wherein the position control mechanism comprises a threaded rod and wherein the plate comprises a threaded opening for receiving the threaded rod.
 7. The assembly of claim 1 wherein the bone-removal device comprises a plurality of pivot pins for engaging a plurality of pivot slots disposed in the guide block.
 8. The assembly of claim 1 wherein the guide block further comprises a means for coupling to the at least one of the guide tracks and a locking mechanism for locking the guide block to the plate.
 9. The assembly of claim 8 wherein the locking mechanism comprises an opening disposed through the guide block and a threaded screw passing through the opening for threading to a threaded opening disposed through the plate.
 10. The assembly of claim 1 wherein the bone removal device comprises a handpiece having a drive connecting portion at the proximal end of the handpiece and a hollow channel extending there from; a tool having a shaft disposed through the hollow channel and a bone-removal element extending from the distal end of the shaft.
 11. The assembly of claim 10 further comprising a positioning portion operatively connected to the handpiece for positioning the bone-removal device in a bone-removal assembly.
 12. The assembly of claim 10 wherein the drive connecting portion is operatively connected to a power source.
 13. The assembly of claim 10 wherein the bone-removal element comprises distal and proximal bone-removal sections having a rectilinear profile and a central bone-removal section having a curvilinear profile.
 14. An assembly for preparing a vertebral disc space to receive a prosthesis, comprising: a sagittal wedge adapted to be disposed between a pair of vertebral bodies; a support frame positioned over the sagittal wedge and adjacent the vertebral bodies; a disc spacer clip positioned over the sagittal wedge and inside the support frame; a tilting guide member having a mounting member, the tilting guide member adapted to be positioned in the disc spacer clip; a transverse unit for mounting to the mounting member, the transverse unit having at least one transverse block; and a bone-removal tool positioned through the at least one transverse block.
 15. The assembly of claim 14 wherein the support frame comprises a plurality of openings formed there through for receiving a plurality of retaining pins to secure the support frame to the vertebral bodies.
 16. The assembly of claim 14 wherein the disc spacer clip comprises a pivot saddle for providing a pivot point between the vertebral bodies.
 17. The assembly of claim 16 wherein the tilting guide member comprises a saddle point at its distal end and a locking mechanism at its proximal end wherein the saddle point and the locking mechanism are connected via the mounting member.
 18. The assembly of claim 17 wherein the saddle point is positioned in the pivot saddle.
 19. The assembly of claim 14 wherein the support frame comprises: a base having a curvilinear profile; at least one lateral support member extending from the base; and an upper support member connected to the at least one lateral support member.
 20. The assembly of claim 16 wherein the disc spacer clip comprises: a lower member forming the pivot saddle; and an upper member adapted to contact the vertebral bodies.
 21. The assembly of claim 20 wherein the upper member of the disc spacer clip further comprises at least one keyway for receiving a shoulder of the sagittal wedge.
 22. The assembly of claim 20 wherein the upper member of the disc spacer clip comprises a support frame interface for connecting the disc spacer clip to the support frame.
 23. The assembly of claim 17 wherein the locking mechanism of the tilting guide member comprises an arcuate track having a means for receiving the support frame in a slideable engagement.
 24. The assembly of claim 14 wherein the mounting member of the tilting guide member comprises a T-track for receiving the transverse unit in a slideable engagement.
 25. The assembly of claim 14 wherein the transverse unit comprises a proximal transverse block and a distal transverse block and a lateral support interconnecting the blocks, each block comprising an opening formed there through for receiving the bone-removal tool.
 26. The assembly of claim 25 wherein the opening of the proximal transverse block is larger in size than the opening of the distal transverse block.
 27. The assembly of claim 26 wherein the proximal and distal transverse blocks each comprise: an outer member having a pair of opposed slots and a mounting slot; an inner member having a pair of angled slots and a pair of opposed pivot slots; and a central member having a pair of pins extending into the angled slots of the inner member and a pair of pins extending into the opposed slots of the outer member.
 28. The assembly of claim 27 wherein the transverse unit further comprises an actuating member connecting the central members of each transverse block.
 29. The assembly of claim 28 wherein the actuating member comprises a rod for threadably engaging the central members of each transverse block and an actuating knob for providing a means for translating the bone-removal tool positioned through the transverse unit.
 30. The assembly of claim 27 wherein the bone-removal tool comprises a pair of pins for fitting to the opposed pivot slots of the proximal transverse block.
 31. The assembly of claim 25 wherein the opening of the distal transverse block has an oblong configuration for guiding the path of the bone-removal tool.
 32. The assembly of claim 24 further comprising a pivot tool having a slot for engaging the bone-removal tool for aiding in the control of the bone-removal tool.
 33. A method for preparing a vertebral disc space to receive a prosthesis, the method comprising: attaching a support frame to a plurality of vertebral bodies, wherein the support frame includes a base and a pair of guide tracks extending from the base and wherein the base is secured to the plurality of vertebral bodies; operatively connecting a guide block to at least one of the guide tracks, the guide block having an opening disposed there through; coupling a position control mechanism to at least one of the guide tracks, wherein the position control mechanism includes a plate extending there from for coupling to the guide track and the guide block and an actuating knob; adjusting the position of the plate and therefore the guide block by adjusting the actuating knob; positioning a bone-removal device through the opening of the guide block; and operatively connecting the bone-removal device to the guide block.
 34. The method of claim 33 wherein the base is secured to an anterior surface of the plurality of the vertebral bodies.
 35. The method of claim 33 further comprising: setting an angle of one of the guide tracks relative to the base.
 36. The method of claim 35 wherein the angle is adjustable between 0 and 90 degrees.
 37. The method of claim 33 wherein coupling a position control mechanism to at least one of the guide tracks further comprises slideably attaching the position control mechanism to the at least one of the guide tracks.
 38. The method of claim 33 further comprising: locking the guide block to the plate.
 39. The method of claim 33 wherein adjusting the position of the plate and therefore the guide block includes threadedly adjusting the position of the plate.
 40. The method of claim 33 further comprising: connecting the bone-removal device to a power source. 